There's now a main ecs.h file that includes the sub-system headers,
removing the need to explicitly include several header files, but the
sub-systems are a less cluttered.
Font cannot be overridden yet, but script attributes (language, script
type, direction) and features can be set at all three levels in a
passage. Attributes on the root level act as defaults for the paragraph
and word levels, and paragraph attributes act as defaults for the word
level.
And add a function to process a passage into a set of views with glyphs.
The views can be flowed: they have flow gravity and their sizes set to
contain all the glyphs within each view (nominally, words). Nothing is
tested yet, and font rendering is currently broken completely.
